Conventionally, measurement has been performed and images obtained utilizing reflected ultrasound waves and the like. For example, with an ultrasound diagnosis apparatus, a tomogram of an organism is obtained by transmitting an impulse wave from an ultrasound transducer, receiving back the reflected echo, and then subjecting it to image processing. For such an ultrasound diagnosis apparatus, the deepest invasion depth and highest resolution possible is required.
There is a pulse compression technique that satisfies this requirement. With this, an originally long pulse is compressed and therefore shortened by subjecting a to-be-transmitted ultrasound signal to FM modulation (hereinafter, the resulting signal is referred to as a chirp signal) and upon reception, passing it through a filter corresponding to the chirp signal. An attempt is then made to increase resolution due to the compression, and at the same time improve the signal-to-noise ratio, and improve the invasion depth.
Pulse compression is widely used with the objective of attempting to increase transmission energy under the limitation of transmission peak-power in the field of radar and sonar in order to increase survey distance and/or gain higher resolution. Much research on introducing the pulse compression technique with similar objectives is also being carried out in the field of medical ultrasound. Notwithstanding benefits such as being able to improve resolution in a predetermined region in order to allow manipulation of the transmission signal spectrum in the time domain, this pulse compression technique has yet to reach realization in the field of medical ultrasound. Diverse research on utilizing the pulse compression technique that is utilized in such field of radar is being carried out in the field of medical ultrasound.